several ways (for different results) to "apply" a paper texture on an existing layer's content,
one of them is to load the paper in its own (top) layer (FX-stack : Color/ Image Source = Paper),
then to apply a Scan-Cleaner FX on it, and turn the layer blending mode to Erase (or merge it to the (below) target layer in "Erase" mode),
Undo, tweak the ScanCleaner profile, and Redo, to modify the texture intensity (effect).

Among the others solutions, you have the Bump FX, or the (directional) Displacement Mapping FX, both are working fine with the source set on "Paper", but will give you different results,
I personally use sometimes a couple of Displacement Mapping FXs, the first one in a diagonal direction, the second one of the same amount but in the opposite direction, it make the drawing lines deformed in regard of the paper texture's depth.
of course, you can mix 2 (or more) FXs to achieve the paper structure simulation, f.i. a Bump + a LumaKey, ... etc...